The most limiting aspect in mobile technology is the electrical power supply. It restricts autonomy and has a direct impact on the weight and size of electronic devices. Most portable devices currently use batteries, although they are not of an environment friendly technology and they add considerable amount of volume and weight to portable devices. On the other hand extreme miniaturization of batteries is not convenient, since these batteries have to be changed frequently by users with limited finger dexterity, in the case of elderly people using hearing aids. Nonetheless, batteries will continue to be the main source of power in the near future, but energy harvesting technologies are gaining interest as alternatives to batteries. Energy harvesters, which obtain energy from external sources such as solar power, thermal energy or human power, provide small amounts of power and are usually suitable for low power portable devices. Wearable and implantable medical devices typically have low power consumption and strict size limitations. Hence, these are devices for which energy harvesting could be successfully applied. Among these types of devices are hearing aids and smart hearing protection devices, also called in-ear devices because they usually fit inside the ear canal. In addition, these have been substantially modified in recent years and are becoming less energy consuming. Furthermore, according to the World Health Organization, hundreds of millions of people are suffering from various types of hearing impairment and tens of millions of hearing aids are currently in use. Considerations such as these encourage further investigation as to using energy harvesting methods to power the electronic circuits of in-ear devices. Since the user wears the in-ear device, one possible power source would be the user and another would be the user's environment. In general, batteries and energy harvesting from the environment or the human body are the only possible ways to power in-ear devices.
Energy harvesting from human power has been extensively done using piezoelectric materials and rotary magnetic generators in relation with the swinging arm, walking (knee articulation and successive compressions of the sole below the ankle, etc.), but all these sources of energy are relatively far from any in-ear device and would nevertheless require wiring connection if used, thus creating discomfort to the user. Furthermore, these harvesting techniques typically generate more energy, namely milliwatts (mW) and more, than are required for a typical active in-ear device (as hearing-aid devices, smart hearing protection devices, and the like), in the order of a few microwatts (μW), but less than 1 mW.
Accordingly, there is a need for an improved energy harvester device for in-ear devices and an active in-ear device with such an energy harvester device therein.